Ink-jet printers have been widely utilized in recent years because of their advantages such as low noises and low running costs. Color ink-jet printers capable of producing color images on a plain paper have also been on sale in the marketplace. It is, however, extremely difficult to meet with all requirements for color reproducibility, water resistance, light resistance, image drying characteristics, prevention of bleeding and reliability of ink-ejection. In particular, in the case of a color printer, image deterioration is apt to take place at red, green and blue regions in which two colors are superimposed, although no such image deterioration occurs in single color printed portions of yellow, magenta or cyan. Especially when ink images on a paper are dried without using any image fixing unit, significant bleeding occurs in the recorded image, even when an improvement in drying characteristics is attempted by increasing the penetrating efficiency of the ink into the paper (Japanese Unexamined Patent Publication No. S55-29546).
Japanese Examined Patent Publication No. 60-23793 describes that an ink containing a dialkylsulfosuccinic acid as a surfactant can improve drying characteristics so that deterioration of image quality is minimized. However, this ink has problems that pixel diameters considerably vary depending on the paper quality, that the image density is considerably decreased and that the surfactant contained in the ink is decomposed in an alkaline environment so that the effect thereof is lost during storage.
Japanese Unexamined Patent Publication No. S56-57862 discloses an ink containing a strongly basic material. While the ink is effective for printing on an acidic paper sized with rosin, no improvement is observed when the ink images are formed on a paper manufactured using an alkyl ketene dimer or an alkenyl sulfosuccinic acid as a sizing agent. Even with an acidic paper, the ink fails to show an effect at image portions in which two colors are superimposed.
Japanese Unexamined Patent Publication No. H01-203483 discloses a recording ink characterized by containing a polyhydric alcohol derivative and pectin. The pectin is added as a thickening agent for preventing the image blurs. However, the pectin is a nonionic material having a hydroxyl group as a hydrophilic group. Therefore, this ink has a problem that the stability in ejection is low when the printing operation is interrupted for a certain period of time.
To cope with the above problems, the currently adopted measure is to use multi-path recording for reducing an amount of ink penetrating into a paper while improving the image density. In attaining high speed printing, however, it is a problem to reduce penetration of an ink into a paper, especially the penetration of an ink in the direction of the thickness thereof at secondary color portions.
Japanese Unexamined Patent Publication No. 2001-55533, and No. 2001-8138 disclose an ink in which a black pigment ink is used for reducing penetration into a paper and for increasing the image density and dye-containing color inks are used for color inks other than black and for increasing penetration into the paper, and in which bleeding in boundaries between the black and other colors is suppressed by reaction. With these inks, however, bleeding cannot be prevented at a high printing speed. The known inks are still not fully satisfactory.
It is, therefore, an object of the present invention to provide an ink set for an ink jet recording process, wherein at least two aqueous inks A and B having different hues are superimposed to form a color image, the ink set being capable of giving a clear color image by high speed printing having good resolution without bleeding in the boundaries between two colors. It is also an object of the present invention to provide a method, an ink cartridge and an apparatus for ink jet recording using the above ink set.